package E;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        String  str=sc.nextLine();
        String result="";
        int n=str.length();
        int i=0;
        int temp=1;
        while (i<n){
            result+=str.charAt(i);
            i+=temp;
            temp++;
        }
        System.out.println(result);
    }
}
